1. Field of the invention
The present invention, in general, relates to a crosslinked, flame-retarded resin composition and the insulated wire having a sheath layer, and particularly to a crosslinked, flame-retardant resin composition capable of protecting a flammable inner material from a direct fire and an insulated wire having a sheath layer using the above composition.
2. Description of the Prior Art
It is known to those skilled to the art that an insulated wire used in high voltage-operating electric equipments such as television sets, microwave ovens, duplicators and etc. has such a structure that an electric wire is coated with an insulating layer which is encapsulated with a protecting sheath layer. As an insulating layer for the insulated wire, there has been used a polymer of polyethlylene or polypropylene. The polymers have such an excellent insulation resistance property that they are endurable to high voltages up to several tens of KVs. Such polymers, however, have a disadvantage of being combustible in themselves. To overcome the combustible property of polyethylene or polypropylene, in general, additives such as flame-retardant fillers or the like are added. The addition of such additives, however, causes to deteriorate the insulation resistance property of the polymers in spite of giving an improvement of flame-retardancy to them. So, the wire coated with the polymers having such additives is not suitable for a high voltage-operating equipment.
In an effort to make up for the deficient property of flammability of the polymers, a material for a sheath layer which protects the flammable insulating layer is made to have an excellent property of flame-retardancy. Polyvinylchloride, crosslinked polyvinylchloride or crosslinked flame-retardant polyethylene has been chiefly used for a conventional sheath layer. When they are made to have a property of high flame-retardancy, mechanical properties and flexibility thereof are deteriorated so largely that the wire sheathed with them is unsatisfactory to be applied to the electric equipments.
In fact, the sheath layer of insulated wire is not necessarily to have high insulation resistance. It is preferable to minimize deterioration of flexibility as much as possible when the material for sheath layer is made to have an excellent property of flame-retardancy. The above mentioned conventional materials for sheath layer have an excellent property of flame-retardancy and yet, do not show good flexibility. Thus, the above mentioned conventional materials are not desirable for sheath materials of insulated wire in the viewpoint of flame-retardancy and flexibility.